SPONGES. 



265 



which long before the creation of Man covered the 

 countries where marble is now found. If this is true, 

 many of the rocks which underlie vast countries, the 

 marble temples and palaces of the East, the marble 

 monuments and public buildings of our own country, 

 the mortar upon the walls and ceilings of our houses, 

 and the marble tables and mantelpieces so highly 

 prized, have all come from the skeletons of these little 

 flowerlike animals of the sea. Their skeletons have 

 furnished even the blocks of marble which the sculptor 

 chisels, and are thus inseparably linked with the highest 

 department of culture and art. 



SPONGES. 



Naturalists formerly believed that Sponges belonged 

 with the Protozoans. But it is now known that they 

 are more nearly related to the Hydroids. The sim- 

 plest sponges are conical or cylindrical in form, hollow. 



^ 'ii Mill 



Fig. 511. — Sponge. 



Fig. 512. — Sponge. Alive. 



with a large opening at the top, while they are 

 attached by the other end to the bottom. The wall 

 of the Sponge is thick and is supported b)' a fibrous 

 skeleton which forms the sponge of commerce. The 



